关于perl 里类的实现的一些疑惑

perlpg

package test1;
sub new{
    my $proto = shift;
    my $class = ref($proto) || $proto;

        my $self = {};
        bless $self, $class;
        return $self;
}

sub ShowME {
        return "Test1\n";
}

package test2;

sub oddness {
        my $class = 'test1';
        my $self = {};
        bless $self, $class;
        return $self;
}

sub createme {
        shift;
        my $self = {};
        $self->{CALLBACK} = shift || sub {print "In call test2\n"};
       
        return bless $self;
}

sub ShowME {
        my $self = shift;
        $self->{CALLBACK}();
        return "Test2\n";
}

package test3;

sub build {
        my $self = [];
        push @{$self}, sub {print shift,"\n"};
        bless $self;
        return $self;
}

sub ShowME{
        my $self = shift;
        print "Me store: @$self\n";
        $self->[0]('in test3 ShowME call.');
        return "Test3\n";
}

package main;

my $t1=test1->new();
print $t1->ShowME;

my $t20=test2->oddness;
print "I call package test2? ",$t20->ShowME;

my $t21=test2->createme;
# 注释/不注释下面一行看不同结果
#$t21->{CALLBACK} = sub {print "Call outside.\n";};
print $t21->ShowME;

my $t3=test3->build;
push @$t3,'+++';
$t3->[0]('in main call.');
print $t3->ShowME();

__END__

上面能说好大一篇了，其实知识就是这样‘试’出来的，想解释的都试试？